Iron making using the conventional blast furnace has the disadvantage of requiring large-scale operation with massive capital input in order to maintain a low cost per ton of metal produced. The process needs lump coke as fuel and reductant. However, the production of coke is costly and subject to environmental problems resulting from the emission of gases such as hydrogen sulphide and because of the formation of air borne dust. The process also needs feed in lump form and current practice is to sinter feed with fluxes. The operation of a sinter plant also involves substantial monetary and environmental costs. In general iron making from the blast furnace process can only be considered for very large plants producing in excess of one million tons per annum of iron.
Electric furnace operations have been developed for smaller plants producing from two hundred thousand to one million tons per annum of iron. The electric furnace operates generally on pre-reduced feed and on scrap iron, and the amount of reduction of iron compounds which takes place is usually a minor component of the process. The process uses coke for this reduction, and thus has the same disadvantages as the blast furnace process. The process also uses electricity for heating purposes, and this is an expensive source of energy for high temperature smelting processes in most locations.
A number of direct smelting processes have been proposed and developed to pilot plant scale, involving the direct combustion of coal in an iron bath or in a slag bath under partial combustion reducing conditions with pure oxygen, or high levels of oxygen enrichment of the injected fuel. These processes have generally involved the use of partially reduced iron-ore as feed, and therefore entail the need for provision of pre-reduction facilities and operations as part of the process. This has necessarily involved greater operating complexity and greater capital costs.
The processes under development generally used bottom tuyeres for injection of fuel, air, and iron source into a metal bath. This entails expensive high pressure injection and involves severe conditions for the refractories in the vicinity of the tuyere. Some processes have used top jetting of fuel and air into the top surface of the bath, but this involves relatively poor heat transfer to the bath and relatively slow smelting reactions.